When building façades are insulated with external wall insulation, the window frames of the building can act as a thermal bridge, because the window frames are generally not covered by the external wall insulation. Heat can, therefore, escape from the building by passing from the building interior through the building wall, into the window frame and to the exterior of the building. Such thermal bridges can undermine the benefit of the new insulation.
In order to reduce the thermal bridging effect of the window frames, the windows are often replaced when the external wall insulation is installed. The new windows are often shifted outwards and arranged so that they are in line with the new façade front. This reduces thermal bridging by preventing contact between the window frame and the building wall itself.
However, in order to fix the new windows in place securely, in particular so that the building meets fire regulations, it is often necessary to fix the window in its new position with brackets, which are attached to the window frame at one end and the reveal or window opening in the building wall at the other. In order to provide sufficient support for the window frame, these brackets must be very strong. They are, therefore, generally metal brackets which form a thermal bridge between the window frame and the building wall. Furthermore, since the brackets are attached to the reveal of the building wall, it is necessary to remove the existing window frame before installing the new window frame. This is undesirable, because it leaves the building open to the elements for a period of time. That is particularly problematic when the building remains occupied during the installation process, as is often the case.
DE 20 2008 016 538 U1 discloses an assembly for installation into an opening in a building wall, which includes a facing frame, made from thermally insulating material, which is secured to a frame arranged in the opening of the building wall. The window frame is mounted within the insulating frame.
The insulating frame is attached to the frame arranged in the opening of the building wall. There is also no separation between the plane of the face of the building façade and the window frame. These features make installation of a new window impossible before the existing window is removed.
DE 20 2006 000 4425 describes a frame assembly for sealing a building opening such as a window or door, which comprises a prefabricated insulation system that is integrally joined to a window frame. Brackets are used to fix the window frame itself to the building wall. In this system, the window frame is attached directly to the building wall. Therefore, although installation is quick, a thermal bridge is formed. This system also appears to prevent installation of a new window before the existing window has been removed.
DE 299 05 365 U1 describes a prefabricated thermal insulating element to be placed in the opening in a façade-insulating layer that is aligned with an opening in the building wall. The prefabricated element has a reveal element formed from a thermal insulating material that is attached to a window frame. When the prefabricated element is installed, the window frame sits within the opening of the building wall. This positioning of the window frame makes it impossible to install the prefabricated element before any existing window has been removed.
On the above background the present invention relates in a first aspect to a corner bracket for assembly of two boards of a window mounting collar into a collar corner and for affixing said window mounting collar to an exterior face of a building façade so as to surround a window opening.
Assembly and mounting of the above described window mounting collar on an exterior face of a building façade presents a number of challenges. First, it is desirable to be able to attach the boards to each other to form the collar, either before or during affixing of the collar to the exterior face of the building façade. Further, affixation should be sufficiently strong, and affixing of the boards to each other should preferably be independent from the specific material of the boards, for example from whether it is possible to attach screws to the boards. For example man-made vitreous fibre boards, e.g. mineral wool fibre boards, will not always be able to provide satisfactory affixation of e.g. screws screwed into the boards. Moreover, freedom regarding spacial dimensions of the boards is of value to make in situ adjustment of the dimensions possible. Finally, insulation abilities of the resultant construction are of importance.